Alternating-current motor.



PATENTED NOV. 19, 1907.

G. A. LOHR. ALTBRNATING CURRENT MOTOR.

APPLIOATIOI FILED BEP'I .,7, 1905.

IN VEN TOR.

WI TNESSES:

ATTORNEY CARL ALFRED LOHR, OF SCHENEGTADY, NEW YORK. r

ALTEBNATING-OUBBENT 'uo'ros.

Specification of Letters Patent. Application filed 8optember 7.1905- Serial No. 277 .886.

Patented Nov. 19, 1907.

To all whom it may concern:

Be. it known that I, CARL ALFRED Lona, a

' citizen of the Empire of Germany,- residing in Schenectady in the county of Schenectady and State of New York, have invented certain new and useful Improvements in Alternating-Current Motors, of which the following is a specification.

This invention relates to alternating current motors, and more articularly to rotary field motors in which alternating currents of different phases are used for generating a magnetic rotary field.

The object ofmy invention is to provide simple means of changing the speed of such motors and to do away with the; changing of the number of poles or the use of different stators or rotors. For, this purpose my invention consists of an alternating current motor, which is so arran ed, that the speed of the same may be rea 11y changed as will be more full described hereinafter and finally pointed out in the claims.

In the accompanying drawing, Figure 1 shows ,a diagram of my'improved motor showing the electrical connections used for changing the speed of the same, and Fig. 2 is same parts in the a diagram of the stator and rotor of the same.

Similar letters of reference indicate the different figures of the drawing.

Referring to the drawing A represents an alternating current motor, of which B shows main conductors connected with a threephase alternating current source, forming the networks. Connected with the networks are supply conductors E, E, E, which when in contactwith the double-throw triple pole switch E serve to "energize the stator. Connected with the alternating current source are three other supply, conductors F, F F which when in contact with the double-throw triple pole switch F serve to ener ize the rotor. Auxiliary conductors G, ,G have interposed therein a regulating resistance R, beingircperly connected with the conductors G and thus connected with the switch E, when thrown as shown in the full drawn position of this switch, or connected with the switch F, when thrown as shown in the dotted position of this switch.

H re resents the collector-rings of the motor, an I the brushes.

may be the same or different. D, D, D, are

the switch Interposed in the sup ly-conductors E, E is a reversing-switch ii, which serves to change the direction of rotation of the rotary field generated in the stator, when the switch E is pro the sup ly-com uctors F, F, is a reversingswitch which serves to change the direction of the rotary field generated in the rotor, when theswitch F is properly thrown.

In order to illustrate the application of my invention in a broader scope, I have shown two reversing-switches K and L, which serve to that one of these reversing-switches may be left out, without departing from the spirit of my invention. These reversing-switches may also both be left out, when certain results of my invention are not desired.

The arrangement of my improved alternating current motor differs from the usual construction of the motors hitherto in use therein, that both arts of the motor enerate rotary fields w en supplied from t e alternating current source. The speed of these rotary fields may be either the same or different. The s eed may be difi'eren't by the use of a di erent number of poles, in stator and rotor, as in the present invention, or by connecting the with a source of electricity each having a different periodicity. Also the direction of rotation of the rotary fields in stator and rotor Also two other cases are possible. Either to generate a rotary field in-the stator and connect the rotor with the variable resistances R,- as it is usually done, or connect the stator with the variable resistances R and connect therotor with the current-supply. The motor will have a tendency in this case to run with a speed of the rotary field generated in the rotor, and will. in the first case run with the speed of the rotary fieldgenerated in the stator.

Having for instance a and a rotor of 12 poles, then, by connecting both members of the motor with a source of three-phase alternating current of a he uency of cycles per second, the speed of t e stator-field will be 200 rotations per minute and that of the rotor-field. 600 r. p m.

When only the stator is connected wlth theline by means or havin the switch E make connection with the con uctors E, E, E, and

F is thrown so as to make constator of 36 poles erly thrown. Interposed in roduce the different motors eeds in bot directions, but I wish to be un erstood,

stator and rotor each conductors G, G, G, and thus'connected with the variable resistances R, as shown-in the drawing by the full drawn position of the switches E and F, then the motor will run asynchronously with the speed of the rotorfield, that is, with 600 rotations per minute.

These two speeds of the motor are absolutely asynchronous, that is, by inserting resistance in the member not connected with the line, the speed may be varied or regulated to any desired s 'eed below that of' the rotary-field.

When 0th members, stator and rotor, are simultaneously connected with the line, that is, the switch E making connection with the conductors E, E", E, and the switch F making connection with the conductors F, F F, and when the rotary fields are generated in o posite directions having properly thrown the reversing-switches K an L, then the motor will run synchronously with a speed equ a] to the sum of the rotary field speed, that is 800 rotations per minute. hen the rotary fields in stator and rotor are generated so as to rotate in the same direction, having properly-throwri the reversing-switches K and then the motor will run synchronously with a seed equal to'the difference of the rotary eld speeds, that is, 400 rotations per minute.

Hence two princ ples are apparent: First. The generation of a magnetic rotary field in each of both members of a motor by simultan'eously connecting both members of a motor,

namely stator and rotor. with a source of alternatmg current, the motor acting then as synchronous motor.

Second. The alternatmg connection of but one member of the motor with a source of alternating. current, and the generation of a rotary field in the first named member, and the useof the other satisfacto" w'ay member of the motor as a part in which the,

currents necessary for producing a torque are induced. Themotor acts then as asynchro nous motor.

In the example of a motor having a stator with 36 poles anda rotor with 12 poles and an alternating current line of a periodicity of -60 cycles per second, the two speeds of 400 and 800 rotations per minute are synchronous-and can he 'uently not be attained in a by making the proper connections w on the motor is atv rest. In order to derive-these synchronous speeds by electrical means the 'following operations have to be made. The synchronous speed of 400 rotations per minute can be readily produced formingfirst a similar case one of said members. I These resistances can be short-circuited or switched out of circuit, when the motor has synchronous speed. Furthermore the two attained the desired synchronous speeds of 800 r. p. m. and of 400- v r. p. m. can be electrically derived by producing first one of the asynchronous speeds, viz. 600 r. p. m. or 200 r. p. m.,having only one member of the motor connected with the alternating current source, and then connecting also the other member of the motor first over resistances with the alternating current source and switching these resistances out of circuit when the motor has attained the desired synchronous speed. I have shown such resistances M in Fig. 1 of the drawing as being inserted in-the,sup ly-connections F F F which connect the rotor C with the alternating current line when the switch F is properly thrown, but these rc-' sistances can also be inserted in the supplyconnections E E, E, which supply the stator with alternating currents when switch E is properly thrown. The purpose of these resistancesM is to facilitate the changefrom an asynchronous to; a synchronous s eed and to secure a start" g of the motor om rest up to one of the synchronous speeds.

Additionally these resistances serve to e ualize the field strengths in both members 0 the motor during the regular work as synchronous motor and to avoid cross-current flowin between the circuits of stator and rotor.

ile I have explained the methods of obtaining asynchronous speed by supplying alternating currents to both members of a motor, when the numbers of poles in said members'are different, I wish to be understood that these methods may also be employed when the numbers ofpoles 1n said members are the same, thus producing only one synchronous and one asynchronous speed in the ratio oftwo to one.

in the same way as explained or the higher synchronous speed of 800 r. p. m. in the cited example, or more precisely expressed in the following manner. The synchronous speed of a motor of the class described having the same number of polesin stator and rotor can be derived by connecting first only one member of said motor with the alternating current line, 'thus producin an asynchronous speed and then connectin' also the other memberwith the alternating-current line, having first resistances inserted, and grad- In this f case the synchronous speed ma be obtained ually'lmpressing a second rotary'field upon tained by connectin the satisfactory working of the motor.

'ing voltages of a certain frequenc currents whatever can be produce thereby,-

the other member. Furthermore the synchronous speed .of such motor may be obsimultaneously both members with the a ternating current line, having resistances inserted in the supplyconnections to one member of said motor.

As for the ratio of numbers of poles in the 'two members of the motorwhen-different numbers have to be used--Iv have so far tacitly assumed that a ratio of one to three is feasible for both princi les, viz. the generation of rotary fields in 0th members of the motor as well as the alternate connection of but one motor-member with an alternating current source.

To show the feasibility of this ratio of polenumbers in the two motor-members in the manner described I refer to Fig. 2 of the drawing. In Fig. 2 I have shown a stator B having 12 oles, as represented bythe heavy lines N an S (north and south poles) on the inner circumference of the stator and a rotor C having 4 poles similarly represented on the outer circumference of the rotor. The-poles on both of these members are distributed around the circumference in equal distances from each other, and the oles of the one member have an angular poih-width equal to that of the other member. Thus it will be seen that with the ratio of one to three between the pole-numbers of both members the result is, that all les of the rotor are facing o posite poles 0 the stator, while two thirds of the poles of the stator are left blank or inoperative.

The factthat opposite poles of stator and rotor are facing each other warrants a satisfactory operation as synchronous motor (Principle 1') and therefore a priori a satisfacto working as asynchronous motor (Princip e 2). Relatin however, to the statorpoles which are ieft blank, naturall .the question may arise whether these po es do not produce induction currents in the rotor of a frequency different from the line freuency, and whether these currents would not distort the wave-shape of the alternating currents in the line or in some way affejct n fact, the blank stator-poles induce alternatbut no as these induced voltages are always in opposition to eachother and thus are entirely compensatd- It would lead too far to fully explain the conditions which occur in the case of two magnetic fields of 12 and 4 poles,

as shown in Fig. 2 of the drawing, and 1t may suffice to illustrate these conditions with a simple analogous case. This analogon may be found in a ring-armature with equally distributed turns, returning into themselves, or, in other words, an ordinary ring-armature without connections or brushes. 7 Obviously, if such armature be rotated in a magnetic every different .method of deriving said field of whatever number of poles, the induced voltages will annul each other, as no connectionsneit-her stationary nor shiftingare provided mature-winding. Similar conditions are met at proper points of the arwith in the case shown in Fig. 2, and my previous assumption of a feasible ratio of poles of one to three in the two motor-members proves therefore as being correct. Furthermore, as for the ratio of the numbers of poles in the two motor-members, I wish to point out that a ratio of one to three, as explained and illustrated in Fig. 2 is by no means the only possible. ratio. Generally speaking, number of poles in the two motor-members will produce the pro er motor-s eeds, particularly the async ronous spee s (Principle 2), but not in ever case a satisfactory working of the motor. t is impossible, however, to exhaust in this specififeasible ratios between the pole-numbers of the two motormembers, especially as in this regard a wide field for improvements is open in devising special windings or specialswitching devices, which, as basing upon the principles 'ven in this specification would naturally be m the scope of my invention.

The general application of my invention, therefore, as described in this specification, results in the following different types of alternating current motors: an alternating current motor, roducing two speeds, one asynchronous, t e other synchronous, by connecting alternately either one member alone or both members simultaneously with the alternating current line, and the method of derivin said synchronous speed as described. n alternating current motor, (producing substantia y a synchronous spee by connecting both members simultaneously with the alternating current line, and the synchronous speed as described. These two types of alternating current motors are obtainable by employing the rinciples as described to a motor having t e same number of poles in the two motor-members. By employing the principles as described to a motor having a different number of poles in the two motor-members, the following t pes of alternating current motors can be ob current motor roducing two asynchronous speeds, obtaina le under load, by alternately connecting only one member with the alternating current line and closing the other member upon itself. An alternating current motor producing two asynchronous an two synchronous speeds, by alternately connecting only one member with the alternating current line and closing the other member upon itself, and by simultaneously connecting both members with an alternating current line and changing the direction of rotation of the rotary field in one member and tamed: an alternating current rotary field motor the method of deriving said two synchronous speeds as described. An alternatin current motor, producing substantial] a ow*' synchronous speed, equal to the erence of the rotary field speeds in stator and rotor, and the method of deriving said synchronous speed as described' Having thus described my invention, I claim as new and desire to secure by Letters Patent:

1. In combination with an alternating current rotary field motor having a stator and a rotor, said stator having a number of poles different from the number of poles of said rotor, means for electrically connecting at will said stator or said rotor to a source of electricity.

2. In combination with an alternating current rotary field motor having a stator and a rotor, said stator haviri I 'a number of poles different from the num er of poles of said rotor, means for electrically connecting at will said stator or said rotor to a source of electricity, means for closing the Windi s of said rotor upon themselves, when sald stator is connected to said source of electricit and means-for closing the windi s of said stator upon themselves'when-sai rotor is connected to said source of electricity.'

3. In combination with an alternating having a, stator auna and a rotor, said stator having a number of- I poles different from the number of\poles.of

said rotor, means for electrical] connecting at will either said stator or sai rotor alone,

or said stator and said rotor simultaneously to a source of electricity.

' 4. In combination with an alternating current rotary field motor having a stator and a rotor, said-stator having a number of poles different from the number of poles of said rotor, means for connecting said stator and said rotor simultaneously to the same source of electricity.

5. In combination with an alternating current motor having two members, a stator and a rotor, means for producing a synchronous spe'ed by simultaneously supplying alternating currents to both members of said motor, means for producing an asynchronous speed having only one of said members supmeansfor deriving said synchronous speed by weakening one of the rotary fields which producesaid synchronous speed.

In. testimony that I claim the foregoing as my invention, I have signed my name in presence of two subscribi witnesses.

' CARL A I iRED LOHR'.

Witnesses:

Hans OTIO, I A. Bonommn.

plied by alternating currents and separate 

